Human Skeletal Muscle Mitochondrial Adaptations Following Resistance Exercise Training

Abstract

It is universally accepted that resistance training promotes increases in muscle strength and hypertrophy in younger and older populations. Although less investigated, studies largely suggest resistance training results in lower skeletal muscle mitochondrial volume; a phenomenon which has been described as a “dilution of the mitochondrial volume” via resistance training. While this phenomenon is poorly understood, it is likely a result of muscle fiber hypertrophy outpacing mitochondrial biogenesis. Critically, there is no evidence to suggest resistance training promotes a net loss in mitochondria. Further, given the numerous reports suggesting resistance training does not decrease and may even increase VO2max in previously untrained individuals, it is plausible certain aspects of mitochondrial function may be enhanced with resistance training, and this area warrants further research consideration. Finally, there are emerging data suggesting resistance training may affect mitochondrial dynamics. The current review will provide an in-depth discussion of these topics and posit future research directions which can further our understanding of how resistance training may affect skeletal muscle mitochondrial physiology.

Acute and chronic effects of resistance training on skeletal muscle markers of mitochondrial remodeling in older adults

“…Resistance training has been well recognized as an effective method to increase muscle hypertrophy and strength (Folland & Williams, 2007). However, whether or not RT induces mitochondrial adaptations remains equivocal and poorly investigated, especially in older individuals (Parry et al, 2020). We investigated the acute and chronic effects of RT on markers of mitochondrial content and remodeling in older individuals.…”

“…However, there is a growing body of literature investigating the mitochondrial adaptations to RT in both younger (Alvehus, Boman, Söderlund, Svensson, & Burén, 2014;Lim et al, 2019;Porter, Reidy, Bhattarai, Sidossis, & Rasmussen, 2015) and older (Flack et al, 2016;Manfredi et al, 2013;Miller et al, 2020;Zampieri et al, 2016) participants, with mixed results. As pointed out by Parry, Roberts, & Kavazis (2020), RT may impose a sufficient energetic stimulus to promote mitochondrial adaptations in older participants. Although there is a growing interest in the effects of RT on mitochondrial biogenesis in older participants, there is a paucity of research investigating its effects on markers of mitochondrial remodeling, which is essential for quantity and quality control of the mitochondrial network.…”

Resistance training increases muscle NAD+ and NADH concentrations as well as NAMPT protein levels and global sirtuin activity in middle-aged, overweight, untrained individuals

“…To this end, several resistance training studies have reported that mitochondrial density remains unaltered [28][29][30] or decreases [31][32][33][34][35], and fewer studies have shown resistance training increases mitochondrial density [36]. We recently posited that, while most of the literature indicates mitochondrial density is not affected in younger individuals, resistance training may facilitate this adaption in older and more sedentary individuals due to increased metabolic demand [37]. However, we did not previously speculate that resistance training-induced increases in muscle NAD + concentrations were responsible for this adaptation.…”

Molecular Regulation of Skeletal Muscle Growth and Organelle Biosynthesis: Practical Recommendations for Exercise Training

“…It was demonstrated that resistance training may promote ameliorations in walking endurance, muscle oxidative capacity and strength [ 275 , 276 , 277 ]. In aged people, the benefits of resistance exercise on muscle function were recently attributed to improvement of mitochondrial function, muscle hypertrophy, modulation of myonuclear domain, and newly formed myonuclei, increases of satellite cell-capillary interaction and content [ 49 , 278 , 279 ]. Of note, it appears that Nordic walking also improves lower limb strength, aerobic aptitude, body composition, life, and sleep quality in old people [ 280 ].…”